There are some technical design solutions that may play a useful part.
High Streets are often significant traffic routes and sometimes the needs of through-traffic over-rides the needs of the street. Reducing the space allocated to running lanes can free space up for parking/pavements etc. The Manual for Streets provide a policy-basis for this which did not exist until a few years ago.

There should be scope for prioritising parking space- wherever it is located - for shoppers using time-stamped tokens or suchlike that can be given to customers (printed on their receipts?) that smart parking meters etc can recognise in lieu of payment.

How we allocate space in our town centres can speak volumes for our priorities - as DaiGwynne suggests it is remarkable how much is tarmac and tyres. I liked this simple compare and contrast image from the US http://www.pps.org/graphics/upo-pages/chart

Tim - easier said than done I know but the neighbourhood boundaries for neighbourhood plans are for the community to decide and not the council. You need to get in there with propsoals for an area and a forum which challenges the conventional thinking if it doesn;t work for your part of London. Technically, the Community Infrastructure Levy can’t come to neighbourhood forums but you are right that many councils will, in effect, give control over a large part of it to them.

It is an interesting debate about what people use the high streets for. The high street is about civic amenity and civic exchange of which shopping is only one part. The other uses that Tony mentions are also very important and in danger of being lost. Its ‘civic-ness’ that needs to be promoted to keep town centres vibrant and I like the idea of ‘civic glue’

Ironically, it was in Tunbridge Wells (Greg Clark’s (planning & localism Minister) constituency) where the council itself was trying to move the civic buildings out-of-town - caused an uproar and it now has a new leader!

Thanks everyone - it was a lively discussion and some great advice and experience. Let’s get going on the “civic glue”! And don’t fortget to feed in any more thoughts by 28 August to shape the Portas review

Just another useful resource to mention: The Meanwhile Project was set up in 2009 to help communiites make temporary use of vacant property pending its reoccupation, refurbishment etc. Their site is at http://www.meanwhile.org.uk/ Resources include a maual for those considering making temporary use of a vacnat shop, which might be particularly relevant for High Street viabilioty. See http://www.meanwhile.org.uk/useful-info/manuals/shop-manual